Computers typically include devices that store data, such as memory devices. A first type of memory device is referred to as a programmable read only memory (PROM) device. To render PROM devices programmable, some PROM devices are provided with an electrical connection in the form of a fusible link, which is also typically referred to as a fuse. Such PROM devices may be programmed by selectively blowing (i.e., creating a discontinuity in) fuses to selectively place circuits of the device into or out of electrically conductive contact with one another.
Another type of memory device is referred to as a dynamic random access memory (DRAM) device. DRAM devices may also utilize fuses to provide redundant circuits. As is known in the art, redundancy improves the fabrication yield of high-density semiconductor devices, such as DRAM devices, by making possible the substitution of a redundant program circuit for a failed program circuit that could otherwise render the entire semiconductor device inoperative. The failed circuit may be bypassed (i.e., deactivated) and the redundant circuit programmed (i.e., activated) by selectively blowing fuses of the semiconductor device.
In the past, PROM device programming and DRAM device repairing, as described above, has been accomplished using a laser to selectively blow open fuses. Laser blowing, however, has become increasingly difficult for a number of reasons. First, as semiconductor devices have shrunk in size, fuses have also shrunk, such that fuses are now smaller than the diameter of conventional laser beams. This makes it difficult or impossible to blow a fuse with a laser without inadvertently damaging another part of the fuse or another circuit of the semiconductor device. Second, as semiconductor devices have shrunk in size, the density of fuses (and other circuits) on the devices has increased. However, conventional lasers require excessive silicon space between fuses to avoid damaging neighboring circuits. Lastly, programming or repairing a device by using a laser to blow open thousands of fuses is very time consuming.
As an alternative to using lasers, fuses have been developed that can be blown by supplying a high current to the fuse. These fuses are sometimes referred to as an electrical fuse (e-fuse), and typically have a narrow neck portion between two larger contact regions. Owing primarily to electro-migration effects, voids can be formed inside of metal conductors due to metal ion movement caused by high-density current flow. Because void growth rate is a function of current density and a fuse narrowed neck region with the smallest cross sectional area will experience the highest current density of the fuse, the application of a high enough current across the fuse can cause the neck region of the fuse to blow (i.e., become discontinuous). Thus, by using e-fuses, PROM devices may be programmed and DRAM devices may be repaired by selectively applying elevated current (i.e., programming current) to appropriate fuses.
However, e-fuse generational scaling poses a barrier for such above-described on-chip programming. That is, as the operating voltage of semiconductor devices continues to be scaled down, achieving and controlling sufficiently high programming voltage for blowing fuses becomes increasingly difficult.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.